[tsilva]

Another example is what happened when Linux moved to 3.0; some programs expected a 2.x version, or even 2.6.x, these programs were clearly buggy, as they should check that the version is greater than 2.x, however, the bugs were already there, and people didn’t want to recompile their binaries, and they might not even be able to do that. It would be stupid for Linux to report 2.6.x, when in fact it’s 3.x, but that’s exactly what they did. They added an option so the kernel would report a 2.6.x version, so the users would have the option to keep running these old buggy binaries. Link here.

From: https://felipec.wordpress.com/2013/10/07/the-linux-way/